Answer
General equation is: $a_n=4+3(n-1)$ and
$a_{20}=61$
Work Step by Step
Formula to calculate the nth term of an arithmetic sequence is: $a_n=a_1+d(n-1)$
Here, $a_1: $ First term and $d=$ common difference
Since, we have $a_1=4$
Then, our General equation is: $a_n=4+3(n-1)$
$a_{20}=4+3(20-1)=4+57=61$
